For future reference for all other questions relating to what a lefty should do, you might want to check out R' Paysach Krohn's English-language book on halachos for lefties. It's available free by mail if you call his home; he lives in Queens, New York, and is listed. (Obviously, you might want to pay him for it, and the postage.)
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msh210♦Oct 5 '10 at 15:46

Thanks, for the information, but I know Hebrew better than English (I live in Israel). Also the question is not for me, but for my child, he is currently 4 years old, so I'll find some book in Hebrew, when he would be a bit older. thanks again.
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jutkyOct 5 '10 at 18:35

Which hand a left-handed person should use, depends on which reason a right-handed person is supposed to use their right hand: either because their right hand is more prominent, or because Kabbalistically, the right hand represents the force of Chessed.

The Mishna Berura (4:22) writes that when washing one’s hands, one washes one’s right hand first irrespective as to whether one is right or left-handed. Likewise, everyone should put their right sleeve, etc. in first when getting dressed (See Mishna Berura 2:4). Unlike right-handed people who tie their left shoes first, however, left-handed people should tie their right shoes first (corresponding to which arm they would tie their Tefillin on).